U.S. patent number 4,653,924 [Application Number 06/742,988] was granted by the patent office on 1987-03-31 for rotating analyzer type ellipsometer.
This patent grant is currently assigned to Victor Company of Japan, Ltd.. Invention is credited to Makoto Itonaga, Kanji Kayanuma.
United States Patent |
4,653,924 |
Itonaga , et al. |
March 31, 1987 |
Rotating analyzer type ellipsometer
Abstract
A rotating analyzer type ellipsometer comprises a rotating
analyzer for receiving light which is impinged on a sample with a
predetermined incident angle and reflected by the sample, a rotary
phase detecting apparatus provided so as to rotate unitarily with
the rotating analyzer for generating a rotary phase signal as the
rotary phase detecting apparatus rotates, a rotating mechanism for
rotating the rotating analyzer and the rotary phase detecting
apparatus, a photodetector for producing an output responsive to
light which is passed through the rotating analyzer, and a computer
for obtaining a phase difference between the rotating analyzer and
the rotary phase detecting apparatus from a phase difference
.phi..sub.o with which a difference between an output I.sub.p of
the photodetector and a theoretical value I.sub.o becomes a minimum
or substantially zero by entering into the computer the output
I.sub.p of the photodetector and calculating the theoretical value
I.sub.o while changing the values of the output I.sub.p and an
initial value .phi..sub.o of the phase difference.
Inventors: |
Itonaga; Makoto (Kanagawa,
JP), Kayanuma; Kanji (Kanagawa, JP) |
Assignee: |
Victor Company of Japan, Ltd.
(JP)
|
Family
ID: |
26458755 |
Appl.
No.: |
06/742,988 |
Filed: |
June 10, 1985 |
Foreign Application Priority Data
|
|
|
|
|
Jun 12, 1984 [JP] |
|
|
59-121377 |
Jun 15, 1984 [JP] |
|
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59-123314 |
|
Current U.S.
Class: |
356/369;
356/364 |
Current CPC
Class: |
G01N
21/211 (20130101) |
Current International
Class: |
G01N
21/21 (20060101); G01J 004/00 () |
Field of
Search: |
;356/369,367,364,381,388 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"The Application of Intensity Transients in Ellipsometry" Brusic et
al. Applied Optics, vol. 9, #7, 7/1970, pp. 1634-1639. .
"A Digital Ellipsometer" Abe et al. Japanese Journal of Applied
Optics, vol. 18, #1, 1/1979, pp. 165-167. .
"High Precision Scanning Ellipsometer" Aspnes et al. Applied Optics
vol. 14, #1, 1/1975, pp. 220-228..
|
Primary Examiner: Rosenberger; R. A.
Assistant Examiner: Cooper; Crystal D.
Attorney, Agent or Firm: Andrus, Sceales, Starke &
Sawall
Claims
What is claimed is:
1. A rotating analyzer type ellipsometer comprising:
a rotating analyzer for receiving light which is impinged on a
sample with a predetermined incident angle and reflected by the
sample;
rotary phase detecting means provided so as to rotate unitarily
with said rotating analyzer for generating a rotary phase signal as
said rotary phase detecting means rotates;
rotating means for rotating said rotating analyzer and said rotary
phase detecting means;
a photodetector for producing an output responsive to light which
is passed through said rotating analyzer; and
computer means for obtaining a phase difference between said
rotating analyzer and said rotary phase detecting means from a
phase difference .phi..sub.p with which a difference between an
output I.sub.p of said photodetector and a theoretical value
I.sub.o of said output I.sub.p becomes a minimum or substantially
zero by entering into said computer means the output I.sub.p of
said photodetector and calculating the theoretical value I.sub.o
from an initial value .phi..sub.o of the phase difference
.phi..sub.p while charging the value of the initial value
.phi..sub.o.
2. An ellipsometer as claimed in claim 1 in which said sample
comprises a transparent film on top of a transparent substrate,
said computer means setting the phase difference which is obtained
as an initial value for a calculation of a film thickness.
3. An ellipsometer as claimed in claim 1 in which said
predetermined incident angle .theta. is selected .theta.=tan.sup.-1
n, where n represents the refractive index of the sample.
4. An ellipsometer as claimed in claim 1 which further comprises a
hollow rotary shaft rotated by said rotating means, said rotating
analyzer being provided within said hollow rotary shaft with an
optical axis of said rotating analyzer in coincidence with an axis
of rotation of said hollow rotary shaft, said rotary phase
detecting means comprising a rotary plate provided on said hollow
rotary shaft and means for generating a rotary phase signal
responsive to the rotation of said rotary plate, said hollow rotary
shaft being arranged with the axis of rotation thereof in
coincidence with a center of an optical path reaching said
photodetector from said sample.
5. An ellipsometer as claimed in claim 4 in which said rotating
means comprises a motor having a rotor thereof provided on said
hollow rotary shaft so as to rotate unitarily with said hollow
rotary shaft.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to rotating analyzer type
ellipsometers, and more particularly to an ellipsometer which
detects a phase difference between a rotating analyzer and a rotary
phase detecting apparatus (rotary encoder) and sets an initial
value for measurement calculations of an optical constant, film
thickness and the like.
Generally, an ellipsometer which measures the ellipticity of the
polarized light by use of ellipsometry, has been used
conventionally when measuring the film thickness of a sample, for
example. The ellipsometer is used for such a measurement because
the sample will not be destroyed and it is possible to measure with
a high accuracy the optical constant of the sample and the film
thickness of an extremely thin single layer film by observing the
change in the polarization state of the reflected light from the
sample. An ellipsometer which employs a rotating analyzer is often
used as an ellipsometer for performing such a measurement.
A general film thickness measuring apparatus which uses the
polarization analysis method as the operating principle thereof,
impinges light from a light source on a measuring plate with an
arbitrarily selected incident angle. The measuring plate is formed
with a transparent film on top of a transparent substrate, and the
thickness of the transparent film is to be measured. The light
reflected from the measuring plate is detected in an ellipsometer
of the film thickness measuring apparatus, and a detection output
of the ellipsometer is analyzed in an analyzer system so as to
measure the film thickness of the transparent film.
In this type of a film thickness measuring apparatus, the film
thickness is not measured immediately. First, an amplitude ratio
tan .psi. and a phase difference .DELTA. between two mutually
perpendicular polarized light components of the reflected light
which is obtained when the incident light is reflected by the
measuring plate, are compared. On the other hand, different values
for the film thickness are successively substituted into a
predetermined equation which has a film thickness d as the
parameter, so as to obtain the amplitude ratio and the phase
difference between the two polarized light components by
calculation. It is assumed that the value for the film thickness d
which is substituted into the predetermined equation is the
thickness of the transparent film which is measured, when the
calculated amplitude ratio and the calculated phase difference are
equal to the measured amplitude ratio and the measured phase
difference, respectively (with an error within a tolerance).
In the ellipsometer, the light impinged on the sample surface with
a predetermined incident angle and reflected thereby is impinged on
the rotating analyzer which is provided coaxially to the rotary
encoder, and the light from the rotating analyzer is received by a
photodetector. The incident angle with which the light is impinged
on the sample surface must accurately coincide with the
predetermined incident angle. Further, the accurate phase
difference between the rotating analyzer and the rotary encoder
must be known. These conditions must be satisfied because it is
necessary to first set an initial value for the measurement
calculation by use of the phase difference between the rotating
analyzer and the rotary encoder when starting the measurement of
the optical constant, film thickness and the like.
However, in an optical system in which the incident angle is fixed,
there is no known method of measuring the phase difference between
the rotating analyzer and the rotary encoder provided in the
optical system. Hence, in the conventional ellipsometer, the phase
difference between the rotating analyzer and the rotary encoder is
detected by impinging the light from the light source directly on
the rotating analyzer without by way of a reflecting surface. The
light is a linearly polarized light of which polarization state is
known.
But even in the case of the ellipsometer in which the phase
difference between the rotating analyzer and the rotary encoder is
detected by impinging directly on the rotating analyzer without by
way of the reflecting surface the light from a laser light source
which emits a linearly polarized light the polarization state of
which is known, the light from the laser light source must be
impinged on the sample surface with an incident angle accurately
coinciding with the predetermined incident angle and the reflected
light from the sample surface must be correctly impinged on the
rotating analyzer through a pinhole, when the detected phase
difference is to be used for the actual measurement. Accordingly,
the mounting angles of a part including the light source and a part
including the rotating analyzer must be set to respective desired
mounting angles with an extremely high accuracy, from a state where
the phase difference between the rotating analyzer and the rotary
encoder is detected by impinging on the rotating analyzer the light
from the light source without by way of the reflecting surface and
with optical axes of the two parts coinciding, to a state where the
light from the light source is impinged on the sample surface with
the predetermined incident angle. But there are disadvantages in
that such setting and adjustment are troublesome and difficult to
perform. Moreover, mechanisms for permitting the mounting angles of
the two parts to be variably adjusted with such a high accuracy,
become complex and must be precise. As a result, the degree of
freedom with which the designing may be carried out becomes poor,
and the manufacturing cost becomes high. In addition, the mounting
angles may become out of order and deteriorate the measuring
accuracy. Further, there is a disadvantage in that a difficult
operation of matching the optical axes of the two parts must be
carried out when replacing a worn-out part.
On the other hand, according to the conventional film thickness
measuring apparatus, when the amplitude ratio and the phase
difference of the two polarized light components are taken along
the X and Y coordinates and the film thickness is obtained with
respect to the amplitude ratio and the phase difference is plotted,
the collection of the plots form an oval shape. Thus, two values
for the film thickness exist with respect to one phase difference,
for example. For this reason, the film thickness cannot be obtained
solely from the phase difference, and the film thickness must
always be obtained from the amplitude ratio and the phase
difference. Further, even when the amplitude ratio and the phase
difference change slightly in value, the value of the film
thickness which is obtained changes greatly. As a result, there are
disadvantages in that the film thickness measuring accuracy is
poor, and that it takes a considerably long time to perform
calculations and the like for obtaining the film thickness.
Accordingly, the prevent inventors have previously proposed in a
U.S. patent application Ser. No. 736,938 entitled "Film Thickness
Measuring Apparatus" a film thickness measuring apparatus which
impinges light from a light source on a transparent film with an
incident angle .theta. equal to or approximately equal to a
polarizing angle .theta. (.theta.=tan.sup.-1 n) which is determined
by the refractive index n of the transparent film and measures
light reflected by the transparent film. As will be described later
on in the present specification, the present invention is suited
for application to this previously proposed film thickness
measuring apparatus.
Further, in a conventional rotating analyzer type ellipsometer, the
axes of rotation of the rotating analyzer and the rotary encoder
are independent of each other. In this conventional rotating
analyzer type ellipsometer, the rotational force is transmitted
from a rotary shaft of a motor to rotary shafts of the rotating
analyzer and the rotary encoder by use of gears or timing belts,
for example, since the axes of rotation of the rotating analyzer
and the rotary encoder are independent of each other. In the case
where the rotational force is transmitted by use of gears, an error
is introduced between the rotary angle of the rotating analyzer and
the rotary angle of the rotary encoder due to eccentricity and
backlash of the gears. On the other hand, in the case where the
rotational force is transmitted by use of timing belts, an error is
introduced between the rotary angle of the rotating analyzer and
the rotary angle of the rotary encoder due to the expansion and
contraction of the timing belts. For these reasons, it is
conventionally impossible to obtain a highly accurate measured
result, and there was a demand for eliminating this problem.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to
provide a novel and useful rotating analyzer type ellipsometer
which can set the initial value described before.
Another and more specific object of the present invention is to
provide a rotating analyzer type ellipsometer which detects the
phase difference between a rotating analyzer and a rotary encoder
and sets an initial value.
Still another object of the present invention is to provide a
rotating analyzer type ellipsometer suited for use in the
previously proposed film thickness measuring apparatus in which
light is impinged on a transparent film with an incident angle
.theta. set equal to a polarizing angle (.theta.=tan.sup.-1 n)
which is determined by a refractive index n of the transparent film
the thickness of which is to be measured.
A further object of the present invention is to provide a rotating
analyzer type ellipsometer in which the rotating analyzer and the
rotary encoder are provided coaxially.
Other objects and further features of the present invention will be
apparent from the following detailed description when read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram for explaining a measuring plate and the
polarized light;
FIG. 2 generally shows an embodiment of a film thickness measuring
apparatus applied with the rotating analyzer type ellipsometer
according to the present invention;
FIG. 3 is a graph for explaining the phase difference;
FIG. 4 is a flow chart for explaining the operation of a computer
of the apparatus shown in FIG. 2; and
FIGS. 5A and 5B are a side view and a plan view in a horizontal
cross section along a line VB--VB in FIG. 5A respectively showing
an embodiment of a concrete construction of the ellipsometer
according to the present invention.
DETAILED DESCRIPTION
First, a description will be given with respect to a measuring
plate the thickness of which is to be measured by a film thickness
measuring apparatus applied with the ellipsometer according to the
present invention, and an incident angle of light impinging on the
measuring plate, by referring to FIG. 1.
A measuring plate 10 comprises a transparent film 12 formed on top
of a transparent substrate 11. The transparent film 12 has a
thickness d which is to be measured. When incident light 13 is
impinged on the measuring plate 10 with an incident angle .theta.,
a part of the incident light 13 is reflected by the surface of the
transparent film 12. The remaining part of the incident light 13
enters within the transparent film 12 and is reflected by the
surface of the transparent substrate 11, and is then directed out
of the transparent film 12 as reflected light 14. When a direction
including the incident plane of light is represented by P (P-axis)
and a direction perpendicular to the direction P is represented by
S (S-axis), the polarization state of light can be described by a
superposition of vibrations of light in two planes in the
directions P and S.
For example, the transparent film 12 of the measuring plate 10 is a
photoresist film which is formed on top of the transparent
substrate 11. The transparent substrate 11 is a glass substrate,
for example. The extinction coefficient (k) of the transparent film
12 and the transparent substrate 11 is equal to zero or an
extremely small value.
The reflected light 14 is subjected to the effects of the thin film
interference. Thus, when a Fresnel reflection coefficient of the
measuring plate 10 with respect to the incident light 13 having the
plane of vibration in the direction P is represented by R.sub.p and
a Fresnel reflection coefficient of the measuring plate 10 with
respect to the incident light 13 having the plane of vibration in
the direction S is represented by R.sub.s, the reflection
coefficients R.sub.p and R.sub.s are dependent on the film
thickness d. In other words, the reflection coefficients R.sub.p
and R.sub.s are described by Fresnel reflection coefficients of
air, the transparent film 12, and the transparent substrate 11. The
reflection coefficients R.sub.p and R.sub.s can be described by the
following complex numbers when equations describing the Fresnel
reflection coefficients are substituted into the reflection
coefficients R.sub.p and R.sub.s.
The above equations (1) and (2) indicate that with respect to the
incident light 13, the amplitude of the reflected light 14 becomes
r.sub.p times and r.sub.s times and the phase of the reflected
light 14 shifts by .DELTA..sub.p and .DELTA..sub.s in the
directions P and S, respectively. A ratio of the reflection
coefficients R.sub.p and R.sub.s can be described by the following
equation (3). ##EQU1## The following equation (4) is obtained when
r.sub.p /r.sub.s =tan .psi. and .DELTA..sub.p -.DELTA..sub.s
=.DELTA. are substituted into the equation (3).
The term tan .psi. describes a ratio of the amplitudes of the
polarized light components of the reflected light 14 in the
directions P and S, and the term .DELTA. describes a phase
difference between the polarized light components in the directions
P and S. Since the reflection coefficients R.sub.p and R.sub.s are
dependent on the film thickness d, the ratio R.sub.p /R.sub.s is
also dependent on the film thickness d.
In order to obtain the film thickness d, the reflected light 14 is
detected, and the amplitude ratio tan .psi. and the phase
difference .DELTA. are measured in a conventionally known analyzing
system. A ratio of the reflection coefficients is obtained by
substituting the measured values into the equation (4). On the
other hand, an arbitrary value for the film thickness d is
substituted into an equation which is obtained by obtaining the
real number portion of the equation (4) (this equation includes the
film thickness d as a parameter), and the value which is obtained
is compared with the value which is obtained by substituting the
measured values. When the two values are not equal to each other,
different values for the film thickness d are successively
substituted into the equation until the two values become equal to
each other with the error being within a tolerance. The value of
the film thickness d which is substituted into the equation when
the two values become equal to each other, is the value of the film
thickness which is to be obtained.
In the previously proposed film thickness measuring apparatus
described before, the incident angle .theta. of the incident light
13 is selected to .theta.=tan.sup.-1 n for the reasons described in
detail in the specification of the previously filed application,
where n is the refractive index of the transparent film 12.
A film thickness measuring apparatus having the incident angle
selected in such a manner, is shown in FIG. 2. A film thickness
measuring apparatus 20 comprises a light source 21 comprising a
HeNe laser, for example. Laser light from the light source 21 is
successively passed through a .lambda./4 plate 22, a polarizer (for
example, a Glan-Thompson prism) 23, and a .lambda./4 plate 24, and
is impinged on the upper surface of the measuring plate 10 with the
incident angle .theta.. The light source 21, the .lambda./4 plates
22 and 24, and the polarizer 23 are unitarily placed on a support
(not shown). The support is set so that the light from the light
source 21 impinges on the measuring plate 10 with the incident
angle .theta.=tan.sup.-1 n as described before.
The incident light is reflected by the measuring plate 10 and is
subjected to the thin film interference. The reflected light is
directed towards an ellipsometer 25. The ellipsometer 25 comprises
a pinhole plate 26, a rotating analyzer 27, a rotary encoder 28, a
pinhole plate 29, and a photodetector 30. The rotating analyzer 27
rotates together with the rotary encoder 28, and the reflected
light is subjected to a time base conversion by the rotating
analyzer 27. Hence, a time-sequential output is obtained from the
photodetector 30.
A Glan-Thompson prism is used for the rotating analyzer 27, for
example. The rotating analyzer 27 and the rotary encoder 28 are
provided coaxially so as to rotate unitarily at a predetermined
rotational speed (for example, several hundred rotations per
minute), and an embodiment of a concrete construction thereof will
be described later in conjunction with FIGS. 5A and 5B. The light
passed through the rotating analyzer 27, passes through a hollow
part of the rotary encoder 28 and reaches the photodetector 30. The
photodetector 30 comprises a silicon photodiode, for example.
The output of the photodetector 30 is converted into a digital
signal in an analog-to-digital (A/D) converter 31. The output
digital signal of the A/D converter 31 is supplied to a computer 32
wherein the predetermined calculation described before is performed
so as to measure the film thickness d. At the same time, the output
signal of the rotary encoder 28 is supplied to the computer 32 as a
timing signal. The measured result is displayed on a display
33.
However, it is difficult to make the direction (direction of a
reference phase point) of the rotating analyzer 27 coincide with
the direction of a reference phase point of the rotary encoder 28
when unitarily assembling the rotating analyzer 27 and the rotary
encoder 28, and the rotating analyzer 27 and the rotary encoder 28
are assembled without making the directions of the reference phase
points thereof coincide with each other. Accordingly, there is a
phase difference between the rotating analyzer 27 and the rotary
encoder 28. When the calculation is performed in the computer 32 in
the state where the phase difference exists, it is impossible to
measure the correct film thickness. Hence, it is necessary to know
the phase difference and set an initial value when performing the
calculation in the computer 32.
Hence, prior to starting the measurement of the film thickness, the
phase difference is measured and an initial value is set as will be
described hereinafter. First, a substrate 10a having a refractive
index n approximately equal to the refractive index of the
measuring plate 10, is positioned in place of the measuring plate
10. When the incident angle is equal to 58.degree., for example, a
glass plate having a refractive index n of 1.6003 may be used for
the substrate 10a.
The polarization state of the light reflected by the substrate 10a
and reaching the rotating analyzer 27 is specified. The intensity
I.sub.o of light after the light has passed through the rotating
analyzer 27 with reference to a direction perpendicular to the
measuring plate 10, can be described by I.sub.o =sin.sup.2 .omega.t
when the amplitude is assumed to be unity, where .omega. represents
the angular velocity of the rotating analyzer 27.
When a phase difference .phi..sub.p exists between the rotating
analyzer 27 and the rotary encoder 28 and it is assumed that the
output signal of the photodetector 30 is read out in synchronism
with the output signal of the rotary encoder 28, an output I.sub.p
which is obtained when the amplitude is assumed to be unity, can be
described by I.sub.p =sin.sup.2 (.omega.t+.phi..sub.p).
FIG. 3 shows the outputs I.sub.o and I.sub.p, and the phase
difference .phi..sub.p exists between the two outputs I.sub.o and
I.sub.p. Hence, prior to measuring the film thickness, the phase
difference .phi..sub.p is first detected. As shown in the flow
chart of FIG. 4, when the operation of the computer 32 is started,
a step 41 enters the output data I.sub.p of the photodetector 30
which is obtained through the A/D converter 31. Next, a step 42
enters an initial value .phi..sub.o of the phase difference. A step
43 calculates a theoretical value of I.sub.o =sin.sup.2
(.omega.t+.phi..sub.o). Then, a step 44 compares the data I.sub.p
and the theorectical value I.sub.o by use of the method of least
squares. Deviations (differences) between the data I.sub.p which is
a function and the theoretical value I.sub.o which is a function,
are obtained and each of the deviations is squared. When a
remainder obtained by adding the squared deviations is represented
by .delta., the theoretical value .phi..sub.o is considered down to
two places of decimals, and the theoretical value .phi..sub.o with
which the remainder .delta. becomes a minimum is looked for. When
the remainder .delta. is not a minimum, a step 45 changes the
initial value .phi..sub.o of the phase difference, and the steps
43, 44, and 45 are repeated. On the other hand, when the remainder
.delta. becomes a minimum, a step 46 uses the initial value
.phi..sub.o which is obtained in the manner described above as the
phase difference .phi..sub.p which is used when meauring the film
thickness thereafter in the computer 32, and sets the phase
difference .phi..sub.p (.phi..sub.o) as the initial value for the
calculation which is performed when measuring the film thickness.
The detection of the phase difference and the setting of the
initial value are completed by the operation described
heretofore.
According to the present embodiment, the incident angle of the
incident light need not be set again when measuring the film
thickness by setting the incident angle .theta. to tan.sup.-1 n as
previously proposed, because the detection of the phase difference
is performed by setting the incident angle .theta. of the incident
light to tan.sup.-1 n. After performing the detection of the phase
difference and setting the initial value for the calculation of the
film thickness, it is possible to start the measurement of the film
thickness without performing any adjustment of the incident
angle.
The ellipsometer of the present embodiment is not limited to the
application to the previously proposed film thickness measuring
apparatus. In addition, the incident angle .theta. is not limited
to a value described by tan.sup.-1 n.
Further, in the present specification and claims, the measuring
plate 10 and the substrate 10a described before will be referred to
by a general term "sample".
Next, a description will be given with respect to an embodiment of
the concrete construction of the ellipsometer 25 by referring to
FIGS. 5A and 5B. In FIGS. 5A and 5B, those parts which are the same
as those corresponding parts in FIG. 2 are designated by the same
reference numerals, and description thereof will be omitted.
A photodetector support 52 is fixed on a base 51. In addition, a
support 53 for supporting the driving part of the rotating analyzer
is fixed on the base 51. The photodetector 30, a filter 54, and the
pinhole plate 29 having a pinhole 29a are fixed to the support
52.
A motor case 55 is mounted on the support 53. A pinhole plate
holder 56 which is mounted with the pinhole plate 26 having a
pinhole 26a, is fixed on the motor case 55.
A rotary shaft 59 rotatably supported by a bearing 57 which is
provided on the support 53 and a bearing 58 which is provided on
the motor case 55, has a hollow tube construction. The hollow part
of the rotary shaft 59 constitutes an optical path.
A rotor (permanent magnet) 60 is fixed to an intermediate part 59b
of the hollow rotary shaft 59. A stator 61 is provided in
correspondence with the rotor 60. A rotary plate 62 of the rotary
encoder 28 is fixed to a tip end part 59a of the hollow rotary
shaft 59. When the rotary plate 62 of the rotary encoder 28 rotates
unitarily with the hollow rotary shaft 59, the rotary encoder 28
generates from a signal generating part 63 an electrical signal
responsive to the rotary angle of the hollow rotary shaft 59 in
correspondence with a predetermined pattern provided on the rotary
plate 62.
In the case where the rotary encoder 28 is an optical type rotary
encoder, an optical pattern is provided along the circumference of
the rotary plate 62 with a predetermined interval, and the signal
generating part 63 is constituted by a light emitting part and a
light receiving part for optically reading the optical pattern. On
the other hand, in the case where the rotary encoder 28 is a
magnetic type rotary encoder, a magnetic pattern is provided along
the circumference of the rotary plate 62 with a predetermined
interval, and the signal generating part 63 is designed so as to
magnetically read the magnetic pattern and generate the electrical
signal. The electrical signal generated from the rotary encoder 28
is amplified in an amplifier 64.
The rotating analyzer (Glan-Thompson prism) 27 is provided in an
inner part 59d of the hollow part (space) in a rear end part 59c of
the hollow rotary shaft 59, so that the optical axis of the
rotating analyzer 27 coincides with the center of rotation of the
hollow rotary shaft 59 and the rotating analyzer 27 can rotate
unitarily with the hollow rotary shaft 59. In other words, the
rotating analyzer 27 is provided in a drum-shaped holder 65. One
end part 65b of the holder 65 is mounted on a rear end part 59e of
the hollow rotary shaft 59 by a plurality of adjusting screws 66.
Springs 67 fitted around the respective adjusting screws 66 exert
urging forces which act in a direction so as to separate one end
part of the holder 65 and the hollow rotary shaft 59. Hence, it is
possible to easily adjust the center of the drum-shaped holder 65,
that is, perform an adjustment so that the center of the rotating
analyzer 27 coincides with the center of rotation of the hollow
rotary shaft 59, by tightening or loosening the adjusting screws
66.
A hole 68 is formed in a central part of a bottom plate 65a of the
holder 65. A hole 69 is formed in a central part of a top plate 65c
of the holder 65.
The pinhole 29a of the pinhole plate 29 and the pinhole 26a of the
pinhole plate 26 are arranged to lie on an extension of the center
line of the hollow rotary shaft 59. Thus, the light reflected by
the sample reaches the photodetector 30 by way of the pinhole 26a
of the pinhole 26, the inner space of the hollow rotary shaft 59,
the rotating analyzer 27, the hole 68, the pinhole 29a of the
pinhole plate 29, and the filter 54 in this sequence.
According to the construction described heretofore, the rotating
analyzer 27 having the optical axis which coincides with the center
of rotation of the hollow rotary shaft 59, rotates unitarily with
the hollow rotary shaft 59. In addition, the rotary encoder 28
which is provided coaxially to the hollow rotary shaft 59 also
rotates unitarily with the hollow rotary shaft 59. For this reason,
the rotary angle of the rotating analyzer 27 and the rotary angle
of the rotary encoder 28 are constantly the same. Therefore, it is
possible to easily obtain a highly accurate measured value by
processing the signal which is generated in correspondence with the
light which reaches the photodetector 30 by way of the optical path
formed in the hollow part of the hollow rotary shaft 59.
Further, the present invention is not limited to these embodiments,
but various variations and modifications may be made without
departing from the scope of the present invention.
* * * * *